1. Field of Invention
The present invention relates to a method for controlling a variable damper in a vehicle, and more particularly, to a method for controlling a continuously variable damper for a vehicle wherein only a front-wheel G sensor can be used to estimate a vertical acceleration value of a rear wheel in a state where a rear-wheel G sensor is removed.
2. Description of the Prior Art
In general, a vehicle suspension system is an important device for connecting a vehicle axle and body and absorbing vibration or shock exerted from a road surface to a vehicle axle to prevent the shock from being transferred directly to the vehicle body. This device provides the following three major functions.
First, the vehicle suspension system provides a passenger with ride comfort by effectively eliminate an irregular input generated from a road surface while a vehicle is traveling. Second, an improved handling performance can be provided by controlling the shaking of a vehicle generated by the driving activity or road unevenness. Third, vehicle stability when a vehicle is cornering, braking and accelerating can be provided by keeping vertical load on a tire contact surface when the vehicle is traveling on an irregular road surface.
In order to detect a motion of a vehicle body, such a vehicle suspension system includes vertical and longitudinal acceleration sensors installed at positions on a vehicle body above respective wheels, ride height sensors installed at the vehicle body to detect the vertical displacement of the suspension system, and four G sensors installed at a variable damper to detect the vertical acceleration of the vehicle body and wheels. Further, the suspension system utilizes auxiliary signals including vehicle speed signals, braking signals, steering angle signals and the like in order to properly perform the suspension control.
In addition, in order to perform the suspension control, the MCU receives signals from the respective sensors in the suspension system, applies the received signals to a control algorithm to calculate a suspension force required in respective hydraulic cylinders, and then outputs voltage signals to a voltage amplifier for actuating pressure control valves.
In particular, the four respective G sensors of the variable damper (shown in FIG. 1) installed at the vehicle body and wheels among the components of the suspension system are sensors for implementing the Sky-hook control which corresponds to a basic principle used in a ride control of the continuous damping control system (CDS)
That is, the term ‘Sky-hook’ is used to illustrate the concept that a vehicle is mounted to a virtual sky over the vehicle by means of a damper having a fixed damping coefficient, but this concept cannot be actually implemented. Therefore, the substantially same vibration isolation effect as in the Sky-hook control can be achieved by employing a damper with a damping coefficient that can continuously vary according to the vehicle behavior.
As shown in FIG. 2, the vertical velocity Vs of a vehicle and the vertical velocity Vu of a wheel are required to achieve this vibration isolation effect. That is, the four G sensors capable of measuring the vertical velocity and acceleration are installed at the vehicle body and wheels, respectively, such that the desired respective vertical velocity can be obtained by integrating the signals received from the installed G sensors.
Therefore, in the case of the four, i.e. front/rear and left/right, G sensors installed at the vehicle body, their three points can be positioned on a single plane in a mathematical view. Thus, even though one sensor is eliminated, signals from only the other three G sensors can be used to estimate the vertical acceleration of the position where the G sensor is eliminated. Accordingly, it does not matter to the implementation of the Sky-hook control.
However, since the four, i.e. front/rear and left/right, G sensors installed at the vehicle wheel are subjected to an independent suspension mode and an independent motion, the four sensors cannot be positioned on a single plane. As a result, since all the four sensors should be used to implement the Sky-hook control, the number of parts of vehicles cannot be reduced when mass-producing the vehicles. Accordingly, there is a problem in that a cost for a finished vehicle will be increased and an unnecessary economical burden may thus be imposed on the consumer.